1. Field of the Invention
The present invention relates generally to methods, apparatus and systems for disposing casing sections within subterranean boreholes. Also, the present invention relates to forming barriers for waste management by such improved methods, apparatus and systems, and barriers so formed.
2. State of the Art
Containment, management, and disposal of various types of waste, such as chemical, nuclear, and other potentially harmful types of waste are recognized, longstanding problems. It is also well recognized that buried waste may often include heavy metals such as mercury or cadmium, carcinogenic materials such as trichloroethylene, radioactive materials, or other hazardous substances. Further, hazardous materials within buried waste may be leached (i.e., carried from the waste within a liquid) therefrom, into surrounding soil and into the groundwater. Because water is used for human consumption and for agriculture, contamination of groundwater by leaching is a major concern.
However, the contamination caused by buried waste may not be limited solely to groundwater. For instance, contaminated groundwater may be carried into other waterways such as streams, rivers, and lakes, thus polluting those waterways and leading to poisoning of plant and animal life. In addition, polluted waterways pose a threat to humans as well, particularly in the case of waterways and bodies of water used for recreational purposes or as sources of drinking or irrigation water.
Also, while many of the problems associated with buried waste arise from the effect of leachate on water systems, buried waste may also emit gas phase contaminants that may cause deleterious effects if not contained and managed. For instance, such gas phase contaminants may pollute the soil and the groundwater, and may build up to unsafe pressures which could ultimately result in an explosion, or pollution of the atmosphere by venting of the gas.
Accordingly, a variety of methods and devices have been devised to attempt to resolve the problems related to buried waste. These remedies may be broadly grouped into the categories of remediation and containment. Generally, remediation focuses on processes designed to change the chemical composition of a contaminated material or contaminant to a more benign chemical composition, while containment remedies seek to isolate contaminants and contaminated material within an area or remove them from an area.
Remediation approaches such as biological treatments, thermal processes, and chemical processes may be problematic for a variety of reasons. In particular, many remediation techniques may be expensive and potentially hazardous. Further, it may be difficult to verify the effectiveness of many remediation treatments. Also, determining the proper or optimum remediation technique for a given contamination scenario may be, in itself, a complex and time-consuming process.
Containment, barrier, or in situ, approaches may be problematic as well. One known containment approach is simply to dig up and remove the contaminated soil for treatment and/or disposal. This approach is expensive and time-consuming and often accomplishes little more than moving the problem to another location. Of course, finding an acceptable ultimate disposal location is another significant impediment to movement of a contaminated region. Other containment approaches involve installing vertical barriers, horizontal barriers, or both types of barriers around the buried waste. In theory, this approach is attractive because it does not require digging up or otherwise disturbing the buried waste.
However, conventional containment or barrier systems suffer from a variety of inadequacies including a lack of durability, corrosion resistance, and structural integrity. These inadequacies are a function of numerous factors associated with the environment in which the containment or barrier systems are located including, but not limited to: exposure to harsh chemicals such as concentrated saline solutions, saturated calcite and gypsum solutions; exposure to extreme thermal gradients; and exposure to stresses induced by shifting in the earth within and adjacent the contaminated area. In addition, conventional barrier systems may suffer from inadequate ability to monitor or verify the integrity thereof as well as inadequate reparability thereof if a failure should occur.
Accordingly, recently, containment systems that are designed to contain, collect, or process effluent which would otherwise escape from a zone containing waste materials, have been developed. One such containment system is disclosed in U.S. Pat. No. 6,575,663 to Kostelnik, et al., assigned to the assignee of the present invention, the disclosure of which is incorporated in its entirety by reference herein. More particularly, U.S. Pat. No. 6,575,663 discloses a barrier comprising a series of adjacent casing strings that are interlocked with one another and may be filled with a barrier filling material to form a substantially continuous wall. Casing strings are disclosed as being disposed within the subterranean formation by way of so-called “microtunneling” techniques.
Since microtunneling was developed, it has been extensively used for the installation of new pipeline infrastructure, particularly for the water industry in a variety of subterranean formation types, including ironstone, sandstone, shale, clay, and sand. Conventional microtunneling involves the construction of a bored hole by way of a rotating cutting structure disposed on the forward end of a microtunneling machine and forcing the microtunneling machine along a tunneling path with a casing jacking apparatus that provides force to thrust the assembly of a casing string and a microtunneling machine into the subterranean formation. Casing sections may either be jacked in directly behind the microtunneling apparatus or, alternatively, may be jacked into a borehole subsequent to formation thereof. In addition, compressed air or slurry systems for removing cuttings as the microtunneling apparatus advances within the formation may be employed.
FIG. 1A illustrates a schematic side view of a conventional microtunneling apparatus 10 during use, conventional microtunneling apparatus 10 including a pipe jacking apparatus 11, a casing string 17 formed of casing sections 15 which are affixed to one another in an end-to-end relationship, and a microtunneling machine 18.
FIG. 1B shows an enlarged, side cross-sectional view of conventional microtunneling machine 18. Microtunneling machine 18 may include a rotatable portion 114 and a stationary portion 115. Torque may be applied to rotatable portion 114 of microtunneling machine 18 by way of a hydraulic motor (not shown) which is responsive to a sufficient flow of pressurized fluid into port 124 or may be configured to rotate by way of an electric motor or a combustion engine, without limitation. In such a case, port 124 may be configured to accept electricity, fuel, or both, to the microtunneling machine 18.
Rotatable portion 114 may be affixed to shaft 126, wherein shaft 126 may be configured with impeller-type features 127 which may be configured to rotate with rotatable portion 114, so as to push cuttings from the subterranean formation out through port 122 as the microtunneling machine 18 advances into a formation during use. In addition, microtunneling machine 18 may include cutting structure 116 disposed upon the leading end 120 of rotatable portion 114, the cutting structure 116 configured for rotating about longitudinal axis 111. Microtunneling machine 18 may also include a trailing end 118 for connection with casing sections 15 or other structural members.
Pipe jacking apparatus 11 may be disposed within a launch pit 9 and may include frame 25 to which a hydraulic power unit 23 is affixed and one or more hydraulic pistons 20 are movably affixed by rods 22 to a forcing plate 21. More particularly, as shown in FIGS. 1C and 1D, forcing plate 21 of pipe jacking apparatus 11 may be caused to move along frame 25 and apply force to the end 29 of the casing section 15 extending from borehole 14 away from entry point 16 (FIG. 1A). FIG. 1C shows forcing plate 21 in a contracted state, wherein its position relative to frame 25 may be illustrated by distance x1. FIG. 1D shows forcing plate 21 in an expanded state, wherein its position relative to frame 25 may be illustrated by distance x2. Once forcing plate 21 is positioned at distance x2, it may be retracted to distance x1, and another casing section (not shown) may be disposed between the end 29 of the existing casing section 15 and the forcing plate 21. Further, the two casing sections 15 may be affixed to one another by threaded connection, welding, or mechanical fasteners. Of course, repeatedly cycling the forcing plate 21 between positions corresponding to x1 and x2, while installing additional casing sections 15 may incrementally form a casing string providing a casing-lined borehole 14.
Further, additional equipment such as hydraulic power units, fluid delivery systems, and fluid recovery and processing systems may be utilized to supply microtunneling machine 18 with electricity, combustible fuel, pressurized fluid, or compressed gas for causing rotation of the leading end 120 thereof and to remove cuttings that are generated as microtunneling machine 18 progresses through formation 13, as known in the art. Pressurized fluid or compressed gas may be supplied by conducting lines that follow within casing string 17. Also, the drilling path of microtunneling machine 18 may be directionally controlled or guided as known in the art.
Thus, conventional microtunneling apparatus 10 may be utilized to form a casing-lined borehole 14 underneath formation 13 by advancing hollow casing sections 15 through formation 13 from entry point 16 to exit point 19. Conventional microtunneling systems, while enjoying relative success, rely on casing sections 15 that are able to withstand the stresses generated therein by the forces applied thereto by pipe jacking apparatus 11. Generally, the stresses experienced by the casing sections 15 may be compressive in nature, since the pipe jacking apparatus 11 may force the casing sections 15 into the formation 13 against both friction and the forces of microtunneling. However, higher stresses may develop between casing sections 15 in response to connections between casing sections 15 and bending of the casing string 17 to accomplish directional microtunneling.
Therefore, conventional microtunneling apparatus and processes may be currently limited in materials that are suitable for use in forming casing sections 15. Specifically, materials having a relatively high compressive strength, such as steel, may be used in combination with conventional microtunneling apparatus successfully. However, due to the magnitude of the forces applied to casing sections 15 during conventional installation and pipe jacking, many materials that may be superior, at least in some respects, to conventional metal casing sections, but may exhibit lower compressive strengths than are necessary to withstand the forces generated by pipe jacking, may not be employed by conventional microtunneling systems. For instance, a wide variety of polymer materials may exhibit corrosion resistance superior to the corrosion resistance exhibited by steels or stainless steels but may not possess compressive strengths that are required for successful placement within a subterranean formation according to conventional processes and apparatus.
In an alternative, conventional approach for disposing a casing string within a subterranean formation, U.S. Pat. No. 6,682,264 to McGillis discloses a method for installation of underground pipe in which a microtunneling apparatus affixed to a pilot tube drills a pilot hole into a surface of a formation and exits the surface of the formation at a different position. Then, a reamer may be installed on the protruding end of the pilot tube and a pipe connected to the end of the microtunneling apparatus may be pulled into the back-reamed hole that is formed as the microtunneling apparatus is retracted through the pilot hole and reams the same, forming a larger size hole for the pipe to fit within. Such a method may be time consuming and more expensive, since initially forming a pilot hole and then reaming through the pilot hole essentially drills the desired path two times.
In view of the foregoing problems and shortcomings with existing microtunneling apparatus, methods, and systems, it may be desirable to provide improved methods, apparatus, and systems for disposing casing sections within boreholes via tunneling methods and apparatus. Also, it may be desirable to form barriers for waste management by such improved methods, apparatus, and systems.